Well bore perforating apparatus



Oct. 11, 1960 s. J. MARTINEZ, JR 2,955,533

WELL BORR PERPORATING APPARATUS Filed Dec. 16. 1954 YA PWR 56 l *54 INVENTOR.

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A TTOR/VEVS Unite WELL BORE PERFORATING APPARATUS Filed Dec. 16,1954, Ser. No. 475,604

1 Claim. (Cl. H12-21.8)

This invention relates to apparatus for perforating the walls of boreholes which penetrate earth formations, and particularly to free-falling perforating apparatus of the above variety.

In the completion of oil well drilling operations, a string or column of casing is often run to the bottom of the well bore and then cement is forced down the casing and into the space between the casing and the surrounding earth formations. In order to produce oil from the oil-bearing strata, the casing and cement are then customarily perforated opposite the oil bearing formation. The perforation is presumed to also extend into the oil bearing formation, providing an enlarged path through which oil may flow from the formation into the casing.

The usual method of perforating well bore Walls is to lower a perforating gun into a well bore to the depth at which the perforating is to take place, and then fire the gun by electrical means from the surface. The gun usually comprises one or more shaped charges disposed at intervals along the gun structure. The gun structure is often made of light structural material which is disintegrated `and dispersed when the shaped charges are exploded. Thus, the gun structure presents no problem of removal when the well bore is later swabbed to clean out the well and induce oil to ilow into the well bore.

When cable suspended perforating guns are fired in well bores the cable is usually mutilated and torn and often becomes balled-up. Since many perforating guns Vare of the type which are lowered through tubing which is of small diameter as compared to the diameter of the casing in the well bore, any balling up or tangling of the cable presents serious problems when an attempt is made to withdraw the tubing from the well bore. In diilicult cases the tubing must be pulled from the Well and the tangled cable drilled out of the bore hole before other well operations can succeed. In any event, whether the tangled cable is iished out or must be drilled out, the additional running time of the drilling rig is expensive. The cost of the damaged cable, too, represents an economic loss in the perforating operation.

An attempt to lessen the damage to the cable from which the perforation gun is suspended is made by loading the well bore with iluid (such as oil or water). Since the required amount of iluid may either be expensive or not readily available, loading the hole prior to perforating is not desirable. Then, too, loading the bore hole with fluid tends to dissipate the force of the perforating charge, which results in decreased penetration of the earth formations by the explosive charge.

Accordingly, a principal object of this invention is to provide improved apparatus for perforating well bore walls which need not be suspended by cables in the well bore.

Another object of this invention is to provide an improved, more economical, self destroying perforating gun which is adapted to be dropped into well bores.

In accordance with this invention there is provided a States atent perforating gun comprising an expendable shaped explosive charge with a mechanical trigger and related ring apparatus at one end of the gun.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

Fig. l is a diagrammatic view showing a perforating gun in accordance with the invention as the gun falls down a well bore just prior to detonating when the gun trigger strikes a plug in the well bore;

Fig. V2 is an enlarged elevational view, partly in section, of a perforating gun in accordance with the invention;

Fig. 3 is an elevational view of a double-triggered perforating gun in accordance with the invention, and

Fig. 4 is a fragmentary View of a modification of the triggering means of Fig. 2.

Referring to Fig. l, there is shown a well bore 10 which extends into the earth 12 and penetrates an oil bearing formation 14. A string of casing 16 extends from the surface 18 at least through the oil bearing formation 14. The lower part of the casing 16 is cemented in place, the cement 20 being disposed between the casing 16 and the wall (including the oil bearing formation 14) of the well bore 10i. A plug 22, which may be either expendable or non-expendable, is set in the casing 16 slightly below the oil bearing formation 14. A perforating gun 24 in accordance with the invention is shown falling down the well bore 10 just before being detonated as the gun 24 strikes the plug 22. The plug 22 is so positioned in the casing 14 that the explosive carried by the gun 24 will be disposed opposite to the oil bearing formation 14 when the gun 24 is detonated.

The perforating gun 24 is shown in more detail in Fig. 2. The perforating gun Z4 comprises an end section indicated generally by the numeral 26 and a structural or frame section, indicated generally by the numeral 28 into which are secured one or more shaped explosive charges 30. The end section comprises a housing 32 of generally cylindrical shape and has a bore 34 extending upwardly from its lower end 36. Three passages, 38, 38', and 38 extend downwardly from Ithe upper end 44 of the end section 26 and communicate with the bore 34 which is axially disposed in the end section 26. The upper part 40 of the bore 34 receives a blank cartridge 42 or other percussion type detonating device. A gasket 48 is provided between the rim of the cartridge 42 and the cartridge chamber part of the bore 34. The lower or outer end 46 of the bore 34 is counterbored to accommodate a firing pin 50.

The firing pin 50 is of cylindrical form and has a tapered end 52 facing the cartridge receiving part of the bore 34. One part 54 of the circumferential surface of the ring pin 5t) is attened or recessed. A set screw or bolt 56 passes through a bore 5S in the wall 60 of the end section 26 and extends into the counterbored part 46 of the bore 34 in alignment with the recessed part 54 of the tiring pin. The firing pin 50 is inserted in the lower end of the counterbored part 46 of the bore 34 and aligned with the ilattened part S4 facing the bore 58. The bolt 56 is then advanced to retain the firing pin 50 in the bore. The recessed part 54 is of sufcient length to permit the tapered end 52 of the tiring pin 50 to strike the percussion cap part (not shown) of the cartridge 42 before being stopped by the bolt S6. The end 62 of the ring pin 50 extends beyond the lower end 36 of the end section 26 of the gun 24 to permit the detonation of the gun 24 by applying pressure on the firing pin 50.

The frame section 2S includes three tubular members 64, 66, 68 symmetrically disposed in a triangular arrangement and supported by the triangular brace 70. The lower ends of the tubular members 64, 66 and 68 are bent inwardly and secured in bushings 72, 74, 76 (which are .threaded in the end section passages 38, 38', and 38) by the couplings 78, 80, 82, respectively. The bushings are hermetically sealed into the passages 38 by bushings 49. The upper ends of the tubular members 64, 66, 68 are bent inwardly to form the upper end of the gun 24 and are secured within a coupling 84, shown in Fig. 1.

The frame section 28 carries at least one shaped charge 30 in a frangible container 86 (usually glass), the container 86 being proportioned to be retained by and substantially between the three tubular members 64, 66, 68. The shaped charge 30 usually includes a booster charge which is disposed adjacent to one of the tubular members 64, 66 or 68, depending onthe direction in which the shaped charge 30 is oriented. It is recognized that in practice a perforating gun usually contains several perforating charges, some of which charges face in different directions.

In order to tire each explosive charge 30, an explosive fuse 88 having a uniform rate of detonation per unit of length, such as prima cord, is threaded through each of the tubular members 64, 66, 68 with the ends of each length of fuse 88 extending into the upper end 40 of the bore 34 which also contains a booster charge 90. The position along the well bore 10 at which the casing, cement, and/or formation will be perforated is determined by a stop means or plug 22 in the bore hole. The bottom of the bore hole may also be used as the stop means, if convenient. Y

If the bottom of the well bore is used Yas the stop means, the length of the firing pin 50 extending beyond the end section 26 may be used to control the distance above the bottom that perforating takes place. For example, a firing pin 2 feet long would cause detonation of the gun 24 while the end section was 2 feet above the bottom of the hole. j

In operation, the firing pin 50 is inserted into the bore 34 and the set screw 56 advanced to retain the firing pin 50 within the counterbored part 46 of the bore 34. The gun 24 is then dropped down the borehole 10 with the firing pin 50 facing downward. When the ring pin 50 strikes the plug 22 or other stop means, the gun 24 is detonated and the perforating takes place. The number of perforations varies with the number of shaped charges 30 secured to the frame section 28. In practice, a 10 ft. long gun 24 is commonly used, with up to 40 charges being secured thereto.

'When the firing pin 50 strikes the cartridge 42, the

firing of the cartridge 42 ignites the booster charge 90,

thereby exploding the prima-cord fuse 88. The explosion of the prima-cord fuse 88 then detonates the shaped charge 30 (or shaped charges) which, as previously mentioned, contains a booster charge (not shown) disposed adjacent to a tubular member (64, 66, or 68) which contains prima-cord. The frame section 28, end section 26, and frangible container 86 of the shaped charge 30, are reduced to small particles by the explosion which occurs when the gun 24 is detonated.

A modification of the perforating gun 24 is shown in Fig. 3. In Fig. 3 the gun 24a has two similar end sections 26a and 2617, each section containing detonating means of the type shown in the gun 24 in Figs. l and 2. This type of gun provides an alternate means for detonating the shaped charges 30. In event the detonating means in the lower end section 26a fails to operate, a ball or other obstacle (not shown) may be dropped down the well bore 10 to detonate the charges by means of the tiring pin 50\b in the upper end section 26b.

The gun 24a also has preferably at least three resilient fins 92 extending along the gun to facilitate the centering of the gun 24a in the well bore 10. The fins also protect the framework of the gun from damage due to collision with the casing 16 or wall 12 of the well bore 10.

Fig. 4 illustrates, partly schematically, a time delay means in the detonating means of the gun 24. A time delay fuse and cap, represented by the box 94 are disposed between the cartridge 42 and the booster charge 90 in the end section housing 32. Thus, in event the cartridge 42 be accidentally fired before the gun reaches the stop means (plug 22, for example), the time delay will permit the gun 24 to come to the proper position in the .Well bore 10 before the gun is red. The arrange' ment of Fig. 4 is illustrative only. For example percussion type delayed detonating units (not shown) in cartridge forms may be used, the end of the cartridge 42 being inserted into the bore V34 and .held there by the bolt of screw 56, as in the case with the ring pin 50. The amount of time delay required is a function of the time required for the gun to fall from the surface to the stop means.

Thus, perforating guns in accordance with this invention provide a safe, accurate means of `forming a perforation which provides a passageway from a well bore into the adjacent earth formations without the use of cables for suspending the gun in location.

I claim:

Free falling apparatus for piercing a well wall comprising two body sections of generally cylindrical form, a plurality of metallic bow-shaped strips extending from one body section to the other body section and secured to peripheral surfaces of said body sections, a tubular frame section secured at each of its ends to one of said body sections, and at least one explosive charge carried by said frame section and having a booster charge disposed adjacent to at least a part of said frame section, each of said body sections having a bore extending from one end of the body section towards said frame section, said bore containing percussion type detonating means including a firing pin which extends from said end of the body section, and a plurality of passages extending from surfaces of said body section and communicating with said bore, said frame section including ya plurality of tubular members the ends of which are adapted to be secured to said body sections and communicate with said passages therein, a detonable fuse extending through at least a part of said tubular members and having one end exposed to said detonating means in each body section, the booster charge being adjacent to a tubular member bearing said detonable fuse.

References Cited in the le of this patent UNITED STATES PATENTS 120,574 Dickey Nov. 7, 18771 1,300,333 Berry Apr. 15, 1919 2,140,813 Ruther et al. -a Dec. 20, 1938 2,562,880 Andrew Aug. 7, 1951 2,621,895 Toelke Dec. 16, v1952 2,669,928 Sweetman Feb. 23, 1954 2,708,408 Sweetman May 17, 1955 2,733,657 Bryant et al Feb. 7, 1956 

